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      <h1 id="Leecode-023-Merge-k-Sorted-Lists"><a href="#Leecode-023-Merge-k-Sorted-Lists" class="headerlink" title="Leecode-023 Merge k Sorted Lists"></a>Leecode-023 <a href="https://leetcode-cn.com/problems/merge-k-sorted-lists/" target="_blank" rel="noopener">Merge k Sorted Lists</a></h1><h2 id="思路："><a href="#思路：" class="headerlink" title="思路："></a>思路：</h2><p><strong>Solution：堆</strong></p>
<h2 id="Java"><a href="#Java" class="headerlink" title="Java"></a>Java</h2><p><strong>Solution : 利用Comparator接口和PriorityQueue</strong></p>
<ul>
<li>需要的参数：<ul>
<li>一个NodeComparator比较node.val的大小</li>
<li>一个dummy node 初始为空节点</li>
<li>一个current node 指向dummy</li>
<li>一个PriorityQueue最小堆队列</li>
</ul>
</li>
<li>步骤：<ul>
<li>首先构造NodeComparator比较node.val的大小</li>
<li>一个current node 指向dummy</li>
<li>遍历k个list中每一个的头结点，如果头结点不为空，都把它放进PriorityQueue形成一个最小堆</li>
<li>如果PriorityQueue不为空，取出其中最小的节点（pqueue.poll()），current指向取出的节点，current向后移动一位; 同时如果取出后这个node的next不为空，那么把next丢进PriorityQueue中</li>
<li>返回dummy.next</li>
</ul>
</li>
</ul>
<a id="more"></a>

<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">Definition for singly-linked list.</span></span><br><span class="line"><span class="comment">pubulic class ListNode&#123;</span></span><br><span class="line"><span class="comment">	int val;</span></span><br><span class="line"><span class="comment">	ListNode Next;</span></span><br><span class="line"><span class="comment">	ListNode(int x)&#123;val = x;&#125;</span></span><br><span class="line"><span class="comment">&#125;</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Solution</span></span>&#123;</span><br><span class="line">    <span class="class"><span class="keyword">class</span> <span class="title">NodeComparator</span> <span class="keyword">implements</span> <span class="title">Comparator</span>&lt;<span class="title">ListNode</span>&gt;</span>&#123;</span><br><span class="line">        <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">compare</span><span class="params">(ListNode a, ListNode b)</span></span>&#123;</span><br><span class="line">            <span class="keyword">return</span> a.val - b.val;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> ListNode <span class="title">mergeKLists</span><span class="params">(ListNode[] lists)</span></span>&#123;</span><br><span class="line">        ListNode dummy = <span class="keyword">new</span> ListNode(<span class="number">0</span>);</span><br><span class="line">        <span class="keyword">if</span>(lists == <span class="keyword">null</span> || lists.length == <span class="number">0</span>) <span class="keyword">return</span> dummy.next;</span><br><span class="line">        <span class="keyword">int</span> size = lists.length;</span><br><span class="line">        ListNode current = dummy;</span><br><span class="line">        NodeComparator cmp = <span class="keyword">new</span> NodeComparator();</span><br><span class="line">        PriorityQueue&lt;ListNode&gt; pqueue = <span class="keyword">new</span> PriorityQueue(cmp);</span><br><span class="line">        <span class="keyword">for</span>(<span class="keyword">int</span> i = <span class="number">0</span>;i &lt; size;i++)&#123; </span><br><span class="line">            <span class="comment">//遍历k个list中每一个的头结点，都把它放进PriorityQueue形成一个最小堆</span></span><br><span class="line">            <span class="keyword">if</span>(lists[i] != <span class="keyword">null</span>) pqueue.add(lists[i]);</span><br><span class="line">    &#125;</span><br><span class="line">        <span class="keyword">while</span>(pqueue.size()!=<span class="number">0</span>)&#123;</span><br><span class="line">            ListNode node = pqueue.poll(); <span class="comment">//取出其中最小的节点</span></span><br><span class="line">            current.next = node; <span class="comment">//current指向取出的节点</span></span><br><span class="line">            current = current.next; <span class="comment">//current向后移动一位</span></span><br><span class="line">            <span class="comment">//同时如果取出后这个node的next不为空，那么把next丢进PriorityQueue中</span></span><br><span class="line">            <span class="keyword">if</span>(node.next!=<span class="keyword">null</span>) pqueue.add(node.next);</span><br><span class="line">        &#125;</span><br><span class="line">        <span class="keyword">return</span> dummy.next;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<h4 id="补充知识"><a href="#补充知识" class="headerlink" title="补充知识"></a>补充知识</h4><p><strong>Comparator</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">interface</span> <span class="title">Comparator</span>&lt;<span class="title">T</span>&gt;</span></span><br></pre></td></tr></table></figure>

<p>1.比较功能，对一些对象的集合施加了一个整体排序 。 可以将比较器传递给排序方法（如Collections.sort或Arrays.sort ），以便对排序顺序进行精确控制。 比较器还可以用来控制某些数据结构（如顺序sorted sets或sorted maps ），或对于不具有对象的集合提供的排序natural ordering 。<br>2.通过比较c上的一组元素S的确定的顺序对被认为是与equals一致当且仅当c.compare(e1, e2)==0具有用于S每e1和e2相同布尔值e1.equals(e2)。<br>3.一般是在比较器例如: Collections.sort(List<T> list, Comparator&lt;? super T&gt; c) ，Arrays.sort(T[] a, Comparator&lt;? super T&gt; c)根据指定的比较器引起的顺序对指定的列表进行排序。 在Comparator比较器中重写int compare(T o1, T o2) 如果遇到数字的比较，直接在方法内返回两个对象的属性的差值，例如o1.getValue()-o2.getValue() 是升序，o2.getValue()-o1.getValue() 是降序；如果遇到字符形式的比较利用compareTo(T o) 方法进行比较，该方法比较从头开始每一个字符，当前者大于后者返回1，当前者小于后者返回-1。</p>
<p><strong>代码举例</strong></p>
<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> java.util.*;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">HashTest</span> </span>&#123;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">static</span> <span class="keyword">void</span> <span class="title">main</span><span class="params">(String[] args)</span></span>&#123;</span><br><span class="line">        List&lt;Node&gt; list = <span class="keyword">new</span> ArrayList&lt;Node&gt;();</span><br><span class="line">        list.add(<span class="keyword">new</span> Node(<span class="string">"yguo"</span>,<span class="number">25</span>));</span><br><span class="line">        list.add(<span class="keyword">new</span> Node(<span class="string">"msdfj"</span>,<span class="number">22</span>));</span><br><span class="line">        list.add(<span class="keyword">new</span> Node(<span class="string">"skf"</span>,<span class="number">20</span>));</span><br><span class="line">        list.add(<span class="keyword">new</span> Node(<span class="string">"sfe"</span>,<span class="number">23</span>));</span><br><span class="line">        System.out.println(<span class="string">"===Age排序==="</span>);</span><br><span class="line">        Collections.sort(list, <span class="keyword">new</span> Comparator&lt;Node&gt;() &#123;</span><br><span class="line">            <span class="meta">@Override</span></span><br><span class="line">            <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">compare</span><span class="params">(Node o1, Node o2)</span> </span>&#123;</span><br><span class="line">                <span class="keyword">return</span> o1.getAge()-o2.getAge();</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;);</span><br><span class="line"></span><br><span class="line">        <span class="keyword">for</span>(Iterator&lt;Node&gt; it = list.iterator(); it.hasNext();)&#123;</span><br><span class="line">            System.out.println(it.next());</span><br><span class="line">        &#125;</span><br><span class="line">        System.out.println(<span class="string">"===Name排序===="</span>);</span><br><span class="line">        Collections.sort(list, <span class="keyword">new</span> Comparator&lt;Node&gt;() &#123;</span><br><span class="line">            <span class="meta">@Override</span></span><br><span class="line">            <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">compare</span><span class="params">(Node o1, Node o2)</span> </span>&#123;</span><br><span class="line">                <span class="keyword">return</span> o1.getName().compareTo(o2.getName());</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;);</span><br><span class="line">        <span class="keyword">for</span>(Iterator&lt;Node&gt; it = list.iterator(); it.hasNext();)&#123;</span><br><span class="line">            System.out.println(it.next());</span><br><span class="line">        &#125;</span><br><span class="line">        System.out.println(<span class="string">"===Age排序==="</span>);</span><br><span class="line">        Collections.sort(list);</span><br><span class="line">        <span class="keyword">for</span>(Iterator&lt;Node&gt; it = list.iterator(); it.hasNext();)&#123;</span><br><span class="line">            System.out.println(it.next());</span><br><span class="line">        &#125;</span><br><span class="line"></span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Node</span> <span class="keyword">implements</span> <span class="title">Comparable</span>&lt;<span class="title">Node</span>&gt;</span>&#123;</span><br><span class="line">    <span class="keyword">private</span> String name;</span><br><span class="line">    <span class="keyword">private</span> <span class="keyword">int</span> age;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="title">Node</span><span class="params">(String name, <span class="keyword">int</span> age)</span></span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.name = name;</span><br><span class="line">        <span class="keyword">this</span>.age = age;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">getName</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> name;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setName</span><span class="params">(String name)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.name = name;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">getAge</span><span class="params">()</span> </span>&#123;</span><br><span class="line">        <span class="keyword">return</span> age;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">setAge</span><span class="params">(<span class="keyword">int</span> age)</span> </span>&#123;</span><br><span class="line">        <span class="keyword">this</span>.age = age;</span><br><span class="line">    &#125;</span><br><span class="line">    <span class="function"><span class="keyword">public</span> <span class="keyword">int</span> <span class="title">compareTo</span><span class="params">(Node other)</span></span>&#123;</span><br><span class="line">        <span class="keyword">if</span>(age &gt; other.getAge())</span><br><span class="line">            <span class="keyword">return</span> -<span class="number">1</span>;</span><br><span class="line">        <span class="keyword">if</span>(age &lt; other.getAge())</span><br><span class="line">            <span class="keyword">return</span> <span class="number">1</span>;</span><br><span class="line">        <span class="keyword">return</span> <span class="number">0</span>;</span><br><span class="line">    &#125;</span><br><span class="line"></span><br><span class="line">    <span class="function"><span class="keyword">public</span> String <span class="title">toString</span><span class="params">()</span></span>&#123;</span><br><span class="line">        <span class="keyword">return</span> <span class="string">"Name "</span>+name+<span class="string">" age "</span>+age;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>

<figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//输出：</span></span><br><span class="line">===Age排序===</span><br><span class="line">Name skf age <span class="number">20</span></span><br><span class="line">Name msdfj age <span class="number">22</span></span><br><span class="line">Name sfe age <span class="number">23</span></span><br><span class="line">Name yguo age <span class="number">25</span></span><br><span class="line">===Name排序====</span><br><span class="line">Name msdfj age <span class="number">22</span></span><br><span class="line">Name sfe age <span class="number">23</span></span><br><span class="line">Name skf age <span class="number">20</span></span><br><span class="line">Name yguo age <span class="number">25</span></span><br><span class="line">===Age排序===</span><br><span class="line">Name yguo age <span class="number">25</span></span><br><span class="line">Name sfe age <span class="number">23</span></span><br><span class="line">Name msdfj age <span class="number">22</span></span><br><span class="line">Name skf age <span class="number">20</span></span><br></pre></td></tr></table></figure>





<h2 id="Python"><a href="#Python" class="headerlink" title="Python"></a>Python</h2><p><strong>Solution :heapq堆</strong></p>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment"># Definition for singly-linked list.</span></span><br><span class="line"><span class="comment"># class ListNode:</span></span><br><span class="line"><span class="comment">#     def __init__(self, x):</span></span><br><span class="line"><span class="comment">#         self.val = x</span></span><br><span class="line"><span class="comment">#         self.next = None</span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">class</span> <span class="title">Solution</span>:</span></span><br><span class="line">    <span class="function"><span class="keyword">def</span> <span class="title">mergeKLists</span><span class="params">(self, lists: List[ListNode])</span> -&gt; ListNode:</span></span><br><span class="line">        <span class="keyword">import</span> heapq</span><br><span class="line">        dummy = ListNode(<span class="number">0</span>)</span><br><span class="line">        p = dummy</span><br><span class="line">        head = []</span><br><span class="line">        <span class="comment">#遍历k个list中每一个的头结点，如果头结点不为空，都把它放进PriorityQueue形成一个最小堆</span></span><br><span class="line">        <span class="keyword">for</span> i <span class="keyword">in</span> range(len(lists)):</span><br><span class="line">            <span class="keyword">if</span> lists[i]:</span><br><span class="line">                heapq.heappush(head,(lists[i].val,i))</span><br><span class="line">                lists[i] = lists[i].next</span><br><span class="line">        <span class="comment">#如果PriorityQueue不为空，取出其中最小的节点</span></span><br><span class="line">        <span class="keyword">while</span> head:</span><br><span class="line">            val,idx = heapq.heappop(head)</span><br><span class="line">            p.next = ListNode(val)</span><br><span class="line">            p = p.next</span><br><span class="line">            <span class="keyword">if</span> lists[idx]:</span><br><span class="line">                heapq.heappush(head,(lists[idx].val,idx))</span><br><span class="line">                lists[idx] = lists[idx].next</span><br><span class="line">        <span class="keyword">return</span> dummy.next</span><br></pre></td></tr></table></figure>

<h3 id="补充知识-1"><a href="#补充知识-1" class="headerlink" title="补充知识"></a>补充知识</h3><h4 id="python高级（堆heapq模块）"><a href="#python高级（堆heapq模块）" class="headerlink" title="python高级（堆heapq模块）"></a>python高级（堆heapq模块）</h4><ol>
<li>一种著名的数据结构是堆（heap），它是一种优先队列。</li>
<li>优先队列让你能够以任意顺序添加对象，并随时（可能是在两次添加对象之间）找出（并删除）最小的元素。相比于列表方法min，这样做的效率要高得多。</li>
<li>实际上，Python没有独立的堆类型，而只有一个包含一些堆操作函数的模块。这个模块名为heapq（其中的q表示队列），它包含6个函数，其中前4个与堆操作直接相关。必须使用列表来表示堆对象本身。</li>
</ol>
<figure class="highlight python"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br></pre></td><td class="code"><pre><span class="line">                              模块heapq中一些重要的函数</span><br><span class="line">                                                       函 数                                                           描 述</span><br><span class="line">                                                      heappush(heap, x)                                        将x压入堆中</span><br><span class="line">                                                        heappop(heap)                                      从堆中弹出最小的元素</span><br><span class="line">                                                        heapify(heap)                                         让列表具备堆特征</span><br><span class="line">                                                  heapreplace(heap, x)                                     弹出最小的元素，并将x压入堆中</span><br><span class="line">                                                      nlargest(n, iter)                                     返回iter中n个最大的元素</span><br><span class="line">                                                        nsmallest(n, iter)                                   返回iter中n个最小的元素</span><br></pre></td></tr></table></figure>


      
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                    </div>
                </div>
            </div>

            <div class="pswp__share-modal pswp__share-modal--hidden pswp__single-tap">
                <div class="pswp__share-tooltip"></div>
            </div>

            <button class="pswp__button pswp__button--arrow--left" title="Previous (arrow left)">
            </button>

            <button class="pswp__button pswp__button--arrow--right" title="Next (arrow right)">
            </button>

            <div class="pswp__caption">
                <div class="pswp__caption__center"></div>
            </div>

        </div>

    </div>

</div>

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/photoswipe.min.css">
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/default-skin/default-skin.css">
<script src="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/photoswipe.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/photoswipe@4.1.3/dist/photoswipe-ui-default.min.js"></script>

<script>
    function viewer_init() {
        let pswpElement = document.querySelectorAll('.pswp')[0];
        let $imgArr = document.querySelectorAll(('.article-entry img:not(.reward-img)'))

        $imgArr.forEach(($em, i) => {
            $em.onclick = () => {
                // slider展开状态
                // todo: 这样不好，后面改成状态
                if (document.querySelector('.left-col.show')) return
                let items = []
                $imgArr.forEach(($em2, i2) => {
                    let img = $em2.getAttribute('data-idx', i2)
                    let src = $em2.getAttribute('data-target') || $em2.getAttribute('src')
                    let title = $em2.getAttribute('alt')
                    // 获得原图尺寸
                    const image = new Image()
                    image.src = src
                    items.push({
                        src: src,
                        w: image.width || $em2.width,
                        h: image.height || $em2.height,
                        title: title
                    })
                })
                var gallery = new PhotoSwipe(pswpElement, PhotoSwipeUI_Default, items, {
                    index: parseInt(i)
                });
                gallery.init()
            }
        })
    }
    viewer_init()
</script>



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